support php7 on v1.0.x branch

src/php/ext/grpc/call.c

src/php/ext/grpc/call.h

src/php/ext/grpc/call_credentials.c

src/php/ext/grpc/call_credentials.h

src/php/ext/grpc/channel.c

src/php/ext/grpc/channel.h

src/php/ext/grpc/channel_credentials.c

src/php/ext/grpc/channel_credentials.h

src/php/ext/grpc/php_grpc.c

src/php/ext/grpc/php_grpc.h

src/php/ext/grpc/server.c

src/php/ext/grpc/server.h

src/php/ext/grpc/server_credentials.c

src/php/ext/grpc/server_credentials.h

src/php/ext/grpc/timeval.c

src/php/ext/grpc/timeval.h

src/php/lib/Grpc/BaseStub.php

src/php/lib/Grpc/BidiStreamingCall.php

src/php/lib/Grpc/ClientStreamingCall.php

src/php/lib/Grpc/ServerStreamingCall.php